1. Field of the Invention
The present invention relates to techniques for a semiconductor device fabricating process for fabricating large-scale integrated circuits including VLSI circuits (very-large-scale integrated circuits) and ULSI circuits (ultralarge-scale integrated circuits) and, more particularly, to a system and a method of diagnosing particle formation to improve device yield when large-scale integrated circuits are mass-produced.
2. Description of the Related Art
A semiconductor device fabricating process for fabricating large-scale integrated circuits, such as VLSI circuits and ULSI circuits, has a plurality of steps including cleaning, oxidation, doping (ion implantation and annealing), thin film forming, lithographic and etching steps to build an integrated circuit on a silicon wafer.
The cleaning step removes contaminants formed by annealing and etching and adhering to the surface of the silicon wafer. The oxidation step forms a thin film for masking or insulation on the surface of the silicon wafer. The doping step dopes the silicon wafer with impurities to achieve various functional effects. The thin film forming step forms a thin film on the surface of the silicon wafer prior to the lithographic process and uses a chemical vapor deposition method (CVD method) using thermal reaction, photochemical reaction or plasma reaction, a physical vapor deposition method (PVD method) or a sputtering method. The lithographic step prints a circuit pattern on a resist film coating the surface of the silicon wafer. The etching step removes portions of a thin film formed on the surface of a silicon wafer not coated with a patterned resist film by etching using chemical reactions.
Generally, a semiconductor device fabricating process including those steps is carried out by a semiconductor device fabricating line constructed by installing, in a series arrangement, the respective reaction chambers of a cleaning system, a thermal oxidation system, an ion-implantation system, a CVD system, an exposure system and an etching system as shown in FIG. 1 illustrating the present invention. As shown in FIG. 1, a silicon wafer 10 having the shape of a circular disk is fed from the feed side of a semiconductor device fabricating line and is subjected to predetermined processes in reaction chambers 1 as the same is conveyed through the reaction chambers 1 to fabricate a plurality of integrated circuits 10a on the silicon wafer 10.
The performance of the semiconductor device fabricating line is evaluated in terms of throughput, process time and device yield (the ratio of the number of acceptable devices to the total number of integrated circuits). Device yield is an important parameter directly dominating the economic effect of the semiconductor device fabricating process. Referring to FIG. 3 showing a diagram of assistance in explaining the change of device yield of a general semiconductor device fabricating process, the rate of increase in the level of integration, i.e., the number of components per IC chip, every several years (about three years) has been about 400%, and semiconductor device fabricating processes of a new generation have been developed, constructed and applied to practical use in cycles of several years. In the initial stage A of practical application of a semiconductor device fabricating process of each generation, device yield is small and improvements are incorporated into the design of circuits and fabricating methods, and the full-scale mass production of semiconductor devices by the semiconductor device fabricating process is carried out in a mass production stage B. Sometimes, device yield drops suddenly as indicated at A1 or a decreases gradually as indicated at A2 in the initial stage A. Device yield in the mass production stage B, as compared with that in the initial stage A, is stabilized and varies in the range of about 80 to about 90%. Sometimes device yield drops as indicated at B1, B2 and B3 in the mass production stage B.
Particle contamination (PC) is a principal cause of device yield reduction among a very large number of causes of device yield reduction. Particle contamination is caused by particles accumulated on and falling off the inner surfaces of walls defining a reaction chamber and those adhering to operators, or particulate of diameters in the range of several micrometers to one nanometer emanating from a vapor phase prevailing in the reaction chamber. If such particles or particulates adhere to the surface of the silicon wafer, defects including pinholes, cracks or projections are formed in a thin film formed on the surface of the silicon wafer. Such defects cause troubles including disconnection, short circuit and deterioration in integrated circuits, and the integrated circuits are unable to function normally.
It has been general practice to detect the occurrence of particle contamination in a semiconductor device fabricating line by sampling some silicon wafers provided with semifinished integrated circuits from the semiconductor device fabricating line and inspecting the surfaces of the sample silicon wafers for particles adhering thereto with a microscope or the like to solve such a problem. Upon the detection of the occurrence of particle contamination through the inspection of the sample silicon wafers, the semiconductor device fabricating line is stopped, all the reaction chambers in steps preceding the step in which the contaminated sample silicon wafers were sampled are cleaned to avoid fabricating defective integrated circuits.
However, such a particle contamination preventing method needs to clean all the reaction chambers in the preceding steps including those not forming particles because the particle contamination preventing method is unable to specify the source and causes of particle formation, and cannot be effective measures to prevent particle contamination attributable to particles which cannot be removed by cleaning. Since the particle contamination preventing method needs to stop the semiconductor device fabricating line operating for mass production and the semiconductor device fabricating line requires much labor for restoration, the rate of operation of the semiconductor device fabricating line drops temporarily to zero and the productivity of the semiconductor device fabricating line is reduced.
Accordingly, it is an object of the present invention to provide a particle formation diagnosing system capable of enabling easy, reliable removal of particles causing particle contamination to improve the device yield of a semiconductor device fabricating line for mass-producing large-scale integrated circuits.
Another object of the present invention is to provide a particle formation diagnosing method to be carried out by the foregoing particle formation diagnosing system in accordance with the present invention.
According to a first aspect of the present invention, a particle formation diagnosing system comprises an operating condition monitoring unit for monitoring operation parameters of a reaction chamber, a particle analyzing unit for monitoring particle formation in the reaction chamber, and a computer system connected to the operating condition monitoring unit and the particle analyzing unit, in which the computer system comprises an operation record recording means for recording data on the relation between operation parameters of the reaction chamber and the amount of particles formed in the reaction chamber, and an operating condition determining means for determining optimum values for the operation parameters which will reduce the possibility of particle formation to the least possible extent on the basis of the data stored in the operation record recording means.
Preferably, the operation parameters to be monitored by the operating condition monitoring unit of the particle formation diagnosing system in the first aspect of the present invention include temperature, pressure and gas supplying condition in the reaction chamber. Preferably, the particle analyzing unit is a differential mobility analyzer (DMA). Preferably, the reaction chamber is incorporated into a semiconductor device fabricating line.
According to a second aspect of the present invention, a particle formation diagnosing method comprises the steps of monitoring operation parameters of a reaction chamber and condition of particle formation in the reaction chamber, recording data on the relation between operation parameters of the reaction chamber, and the amount of particles formed in the reaction chamber when values of the operation parameters of the reaction chamber are changed, and determining optimum values for the operation parameters which will reduce the possibility of particle formation to the least possible extent on the basis of the recorded data.
According to the first and the second aspect of the present invention, the data on the relation between the operation parameters of the reaction chamber and the amount of particles formed in the reaction chamber is recorded, and optimum values for the operation parameters which will reduce the possibility of particle formation to the least possible extent are determined on the basis of the recorded data. Accordingly, particle contamination of the reaction chamber in practical operation can easily and surely be prevented, so that the device yield of the semiconductor device fabrication line in mass-producing operation can be improved.